The present invention relates to an offset preventing liquid supplying device for a toner image fixing device for use in an electro-photographic type image forming device such as a copying machine and the like and also relates to an image forming device provided with the same offset preventing liquid supplying device.
Generally, a toner image fixing device for use in the electro-photographic type image forming device is provided with a pair of fixing rollers both of which abut at their cylindrical surfaces to each other and at least one of which is of the heat-roller type incorporating a heater in its cylindrical body. The heat-roller type toner image fixing device is generally such that a toner image developed on a recording material in an image forming step is fixed thereon by heat while the material passes, being heated, through a nip between the paired fixing rollers. Direct contact of the fixing roller with a toner image developed on a recording material may cause toner particles to adhere to the working surface of the fixing roller, which particles is then undesirably transferred onto a toner image to be fixed on a next recording material.
As such, so-called xe2x80x9coffset tonerxe2x80x9d is apt to occur in the fixing device of the color type image forming device rather than in the fixing device of the monochromatic type image forming device. This is because the fixing device of the color type image forming device must use fixing rollers with a thick rubber coat having a large heat capacity and covering ability to fuse mixed-color toners of a thick and uneven toner-developed image consisting of plural toner layers (e.g., Magenta, cyan, yellow and black layers) by heating. Such fixing rollers may not possess sufficient release ability due to its thick rubber layer.
In the conventional fixing devices of the color-type image forming device, as shown for example in FIG. 1, offset preventing liquid (g) stored in a storage tank (a) being able to supply is sucked by a piezoelectric or electromagnetic type pump (b) disposed above the tank (a) through a tubular piping (c) and applied by an applying means (e) to a working surface of a heat roller (fixing roller) (d). The applying means (e) is provided with a supplying pipe (f) that extends above and along the heat roller body (d) and has plural supplying ports (h) arranged in the same direction thereof to feed droplets of offset preventing liquid (g) onto a felt material (i) and a surface of an applying roller (t). Rotating in contact with the heat roller (d), the applying roller (t) applies a uniform coat of the offset preventing liquid (g) over a whole length of the cylindrical surface of the heat roller (d). An excess of the offset preventing liquid (g) falling from the applying roller is collected in a pan (j) disposed under the heat roller (d), wherefrom it is returned through a tubular return piping (k) to the storage tank (a).
The offset preventing liquid (g) is thus circulated from the storage tank (a) to the applying means (e). When a level of the offset preventing liquid (g) in the storage tank (a) lowered below a specified level, a sensor (s) for controlling the amount of the liquid in the tank (a) actuates to warn the user of the need for supplying the liquid (g) in the tank (a) and/or to temporally stop the toner image forming process.
In the offset preventing liquid supplying device, it is very important to maintain a constant feed rate of the offset preventing liquid to a full length of the working surface of the heat roller (d). A partial break of a coat of offset preventing liquid (g) applied on the working surface of the heat roller in its longitudinal direction may result in wrapping of the recording sheet around the heat roller (d) and/or unintentional transferring of offset toner to an image fixed on a next recording sheet. Partially excessive supplying of the offset preventing liquid to the heat roller (d) in its longitudinal direction may cause leakage of the liquid from the fixing device.
Therefore, the offset preventing liquid supplying device has the pipe (f) with upwardly opening ports (h) made in its wall relative to the applying means (e) as shown in FIGS. 2 and 3 to simultaneously supply the offset preventing liquid (g) through all the supplying ports (h) on the condition that the image forming device is horizontally mounted.
The equally balanced feed of the offset preventing liquid (g) relative to the longitudinal direction of the heat roller (d) is realized by differentiating diameters of the supplying ports on the upstream (front side in FIGS. 4 and 5) and downstream (rear side in FIGS. 4 and 5) sides of the offset preventing liquid supplying pipe (f) as shown in FIGS. 4 and 5. In practice, the offset preventing liquid supplying ports (h) disposed closer to the upstream (front) end of the offset preventing liquid supplying pipe (f) are smaller in diameter and the ports disposed closer to the downstream (rear) end of the supplying pipe (f) are larger in diameter.
Recently, there has been a steady trend of space-saving design (miniaturization) of the image forming devices. As the result, the image-forming devices may be used as mounted at various places including not-horizontal places. Accordingly, it is necessary to consider a margin for tilting angle of the device.
In this instance, the conventional offset preventing liquid supplying device uses a liquid supplying pipe (f) having a series of upwardly opening ports (h) made in its upper wall of the applying means (e). When the image forming device is mounted in a tilted state with the supplying pipe (f) tilted up in the downstream (rear side) direction relative to the length of the heat roller (d), the upstream side (front side) of the supplying pipe (f) is located at a lower level as shown in FIG. 6, resulting in supplying offset preventing liquid (g) merely from the upstream side ports (h). Namely, in this case, the liquid (g) hardly flows out through the downstream side ports (h), causing unbalanced (uneven) supplying of the offset preventing liquid (g) relative to the length of the heat roller (d). In FIG. 6, letter xe2x80x9cnxe2x80x9d designates a horizontal line.
When the image forming device is mounted in a position tilted in the transverse direction perpendicular to the longitudinal direction of the heat roller (d) as shown in FIGS. 7 and 8, the upwardly opening ports (h) in the wall of the supplying pipe (f) may correspondingly reduce their cross-sectional areas, causing reduction of outflows (feeds) though every port (h). Furthermore, no feed of the offset preventing liquid (g) from the downstream side ports (h) may occur because the feed of the liquid (g) through the upstream side ports under a higher pressure is accompanied by forming an air layer (v) due to the viscosity of the offset preventing liquid (g) in the downstream portion of the supplying pipe (f) with a low pressure.
An object of the present invention is to provide an offset preventing liquid supplying device of a toner image fixing device for use in an image forming device, which system is capable of uniformly supplying offset preventing liquid to a working surface of a heat roller with an evenly balanced feed over a full length of the roller irrespective of the tilted state of the image forming device, and an image forming device provided with the same offset preventing liquid supplying device.
The present invention relates to an offset preventing liquid supplying device for supplying offset preventing liquid to a working surface of a fixing roller of an toner image fixing device for thermally fixing a toner image developed on a recording material. This system includes a storage means for storing the offset preventing liquid, a liquid applying means for applying the offset preventing liquid to the working surface of the heat roller and a pump for supplying the offset preventing liquid from the storage means to the liquid applying means. The liquid applying means has a supplying pipe with series of supplying ports made in a wall thereof in the direction of a liquid flow therein from the upstream side to the downstream side. The supplying ports are arranged in such a way that the ports nearer to the upstream end are open at higher levels and the ports nearer to the downstream end are open at lower levels in the wall of the supplying pipe.
The above-mentioned features of the supplying pipe realizes smooth supplying of the offset preventing liquid through the supplying ports being open at lower levels in the wall of the downstream portion of the supplying pipe even if the image forming device such as a copier is placed in a tilted state with the offset preventing liquid supplying pipe sloped up in the downstream direction along the length of a heat roller to be coated with the offset preventing liquid.
In case when the image forming device is used in a state tilting in a direction perpendicular to a longitudinal direction of the heat roller, there is no reduction in cross-section of supplying ports being open at lower positions in the wall of the downstream portion of the supplying pipe. This makes it possible to smoothly feed the offset preventing liquid through the downstream side ports at the lower positions in the wall of the supplying pipe even if an air layer is formed in the downstream portion of the supplying pipe due to the viscosity of the liquid therein while the liquid under a relatively high pressure flows out through the upstream side ports.
This makes it possible to maintain equally balanced feeds of offset preventing liquid from the upstream side ports and downstream side ports along the length of the heat roller.
The locations of the offset preventing liquid supplying ports in the wall of the supplying pipe are more specifically determined as follows:
Namely, each of offset preventing liquid supplying ports are provided in the wall of the supplying pipe in such a way that opening positions of the ports are shifted lower in the direction from the upstream side to the downstream side of the supplying pipe. In this instance, the offset preventing liquid can smoothly flow out through the supplying ports which openings are lowered in the direction toward the downstream end irrespective of the tilted state of the image forming device in which the supplying pipe has a slope with the downstream side up or a slope in a plane perpendicular to the longitudinal direction of the heat roller. Owing to the above, it is possible to maintain evenly balanced feeds of the offset preventing liquid through the supplying ports in both upstream and downstream portions of the supplying pipe.
Each of offset preventing liquid supplying ports are also provided in pairs in the wall of the supplying pipe in such a way that two ports of each pair are located at opposite positions in a section perpendicular to the direction of the liquid flow in the supplying pipe. This not only realizes smooth supplying of the offset preventing liquid through the supplying ports in both upstream and downstream portions but also provides a great advantage in achieving evenly balanced supplying of the offset preventing liquid to a working surface of the heat roller along the full length thereof by supplying through a lower positioned port of each pair when the supplying pipe has a slope in the direction perpendicular to the longitudinal direction of the heat roller.
Specifically, an image forming device provided with the above described offset preventing liquid supplying device of a toner image fixing device can reliably preventing a paper sheet from wrapping around a heat roller due to partially insufficient feed of offset preventing liquid in the longitudinal direction of the heat roller and can surely prevent contamination with offset toner of an image to be fixed on a next paper sheet. It is also capable of reliably preventing leakage of offset preventing liquid fed in excess to a part of the heat roller. All the above features enable the image forming device to achieve an increased reliability of its performance.